When conducting military operations, and particularly airborne military operations, against an underground hardened target it is often difficult to assess the degree of success achieved in neutralizing the target from further enemy use. The outward manifestations of a xe2x80x9csmart bombxe2x80x9d target neutralization that are now familiar to many television viewers (from the video images originating in the early 1990""s xe2x80x9cDesert Stormxe2x80x9d campaign, images wherein a guided bomb is directed into the ventilation shaft of a multi story building and its successful detonation appraised by way of smoke plumes emerging from lower story windows of the building), are often not a usable indicator of intended results when the target is a buried concrete bunker or a munitions magazine or other underground structure. Even in World War II it was common practice to protect such targets with several feet of reinforced concrete (e.g. the German North Sea submarine pens) and to bury this concrete under a sufficient thickness of earth to preclude outward manifestations of an internal munitions detonation event.
In addition to this difficulty arising from the underground and hardened nature of many present day targets it may be appreciated that the gathering of such target damage assessment information is often accomplished from a distant and moving vantage point, i e., from a moving aircraft, an aircraft that has not remained in the target area because of concern for its own safety from ground fire or other hostile threats. Moreover such target damage assessment is often desired in the situation wherein the attacking and assessing aircraft has not been within viewing distance of the target during the entire operation but has remained over the horizon or at some safe distance from the target and its probable defenses during both the weapon launch and success assessment phases of the operation. In any event it is clearly not desirable to require the attack aircraft to either remain in the target vicinity for assessment purposes or for the aircraft to be required to return to the target area for assessment purposes nor especially for a second neutralization attempt-particularly if such a second neutralization is not needed.
Additional considerations in this success assessment sequence include the possible presence of fog, smoke, camouflage, vegetation and other visual assessment hindrances in the region surrounding many targets and the possible use of delayed action or other immediate-signature-absent weapons against certain types of targets. Today of course the gathering of attack success information is also desirably accomplished from even greater distances, i.e., by way of information collected by a satellite in earth orbit; in this instance success assessment is even less reliable if accomplished only by visual means. In solution of these success assessment difficulties it is desirable to use non-visual quantitative information relating to the weapon, especially information relating to events accompany arrival of the weapon at its target, information obtainable from the warhead and its fuze, for success assessment purposes. Such information can be descriptive of events occurring during a brief time interval preceding detonation of the fuze and the warhead charge.
With respect to such non-visual quantitative information it is helpful to realize that in order to achieve most effective neutralization of a hardened target it is desirable for a warhead to detonate only after entering the interior of the target; that is after passing through one or more layers of the target""s structure. Moreover to achieve this detonation it is common to provide a hardened target fuze with a capability to respond to events that accompany arrival at the target, events including warhead penetration of successive layers of concrete for example. An accelerometer-based signal may be used for this purpose and may indicate hardened weapon penetration of soil and layers of concrete for example. Other fuze sensors that may be useful in future weapons include devices indicating the presence of living organisms or particular materials in the environment encountered by the fuze.
Although such event-responsive or environment-responsive signal generating capability within present day smart fuze devices serves a useful purpose in supporting a complex fuze detonation algorithm (including for example supporting an algorithm calling for detonation of the fuze after penetrating a predetermined thickness of soil and two layers of concrete) there has heretofore been no practical way to communicate the same data used by the fuze detonation algorithm to persons interested in weapon success assessment (or similarly to persons interested in fuze algorithm development or warhead defense efforts). The present invention is believed to provide a practical and technically viable response to this communications need. In addition to the acceleration signals used in the fuze algorithm, an indication of the fuze detonation event is considered to be useful information for weapon success evaluation and may also be provided by the present invention.
The desirability of obtaining warhead encounter event information back from a deployed munitions device has doubtless been recognized for some time however the accomplishment of such communication has been hindered by challenging practical problems of an operating environment nature. Not the least of these problems is the fact that a hardened target-penetrating warhead may encounter deceleration impulses measuring in the range of twenty thousand to twenty four thousand times the force of gravity in amplitude (20,000-24,000 G""s) during penetration of for example a two-foot thick reinforced concrete target layer. FIG. 4 herein shows a drawing made in conformance with U.S. Patent and Trademark Office standards from a photograph of the results of such a penetration accomplished by a small cannon launched hardened target penetration weapon. In FIG. 4 the warhead penetration aperture 400, the target reinforcement bars 402 and the spalling failures 404 and 406 of the concrete at the rear face and front face of the test target 412 are visible. The man represented at 408 in FIG. 4 illustrates relative sizes of the FIG. 4 objects. At least some parts of any target event communication apparatus must endure the forces resulting from the deceleration represented in FIG. 4 and the possibly larger forces present during penetration of an even thicker hardened target; this is of course in addition to the acceleration event forces occurring when the weapon is launched from a cannon or other apparatus on an aircraft or on the ground or elsewhere.
In addition to these acceleration/deceleration forces it is of course clear that receiving communication from a warhead used against an above ground target is one matter however receiving such communication from a warhead directed against an underground or subterranean target is another matter, especially since such communication must occur through tens of feet of earth to be practical, and since this earth may be of widely varying physical and electrical characteristics as is found in for example sandy soils, clay soils, limestone layers and under both wet and dry conditions. In addition to the signal attenuating characteristics of these soils such communications must deal with the loading effect such A materials impose on any antenna used for the communication.
Although subterranean signal propagation has heretofore been used, for examples, in the mining and oil exploration and communication fields, in submarine communications and (perhaps somewhat trivially) in pet yard restraint environments these previous forms of subterranean communication are understood to most often involve operating frequencies, i.e., carrier frequencies, located in the hertz, or kilohertz or few megahertz ranges. Such operating frequencies are of little assistance in resolving the present communication need in view of their long wavelength with respect to the physical sizes of practical warhead devices. Indeed the present invention communication is believed to necessitate use of frequencies in at least the UHF or ultra high radio frequency range in response to this warhead physical size limitation and the need for antenna elements of wavelength-related dimensions located on these warheads. This ultra high radio frequency signal range is also found to afford possible communication xe2x80x9cwindowxe2x80x9d electrical characteristics in at least some of the soils contemplated for warhead encounter.
Additional uses of frequencies extending into the microwave region in combination with subterranean antenna elements are also disclosed in the prior art, especially in connection with efforts to extend the useful life of a producing oil well. These uses of radio frequency energy appear largely intended to be of an energy dissipating nature and produce thermal heating of the affected earth components without attempting to communicate information signals.
The present invention provides a practical arrangement for communicating munitions warhead travel experience-related underground data to a remote location for analysis. The invention uses an ultra high radio frequency subterranean link to a repeater located at or above the earth""s surface. The repeater relays the received data to a command center or other selected location by conventional means. The invention addresses questions of signal transmission, communications apparatus hardening and real world environments.
It is an object of the present invention to provide a munitions travel experience history and detonation assurance indications to a remote location analysis center.
It is another object of the invention to provide hardened communication link apparatus capable of surviving in the environment of a hardened target penetration warhead.
It is another object of the invention to provide a subterranean signal communication arrangement usable in a plurality of real world environments.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
These and other objects of the invention are provided by subterranean communicating munitions damage assessment apparatus comprising the combination of:
an obstruction-penetrating munitions warhead having a frontal target engaging portion, a munitions explosive material-container portion and a rearward electrical circuit containment portion;
ultra high radio frequency energy signal generator electrical circuit apparatus contained in a physical shock attenuating suspension in said electrical circuit containment portion of said munitions warhead;
a source of direct current electrical energy contained in physical shock attenuating suspension in said electrical circuit containment portion of said munitions warhead and including energizing connection with said ultra high radio frequency energy generator circuit apparatus;
electrical transducer signal generating apparatus connected to a modulation signal input port of said ultra high radio frequency energy generator circuit apparatus and generating an electrical signal responsive to physical disturbance events attending said munitions warhead;
ultra high radio frequency energy radiating antenna apparatus received in connection with said ultra high radio frequency energy generator electrical circuit apparatus and energized by connection with a signal output port thereof;
portable ultrahigh radio frequency energy signal repeater apparatus having subterranean signal responsive communication link compatibility with said ultra high radio frequency energy generator electrical circuit apparatus;
said portable ultrahigh radio frequency energy signal repeater apparatus being initially contained in segregable connection with said warhead;
control apparatus including an altimeter signal generator connected to commence repeater apparatus segregation from said warhead prior to earth impact.